animated_cross_fade.dart

class MyAnimatedCrossFade extends StatelessWidget {
  const MyAnimatedCrossFade({
    super.key,
    required this.duration,
    required this.index,
    required this.children,
  }) : assert(index >= 0 && index < children.length);

  final Duration duration;
  final int index;
  final List<Widget> children;

  @override
  Widget build(BuildContext context) {
    return Stack(
      fit: StackFit.expand,
      children: [
        for (var i = 0; i < children.length; ++i)
          AnimatedOpacity(
            duration: duration,
            opacity: i == index ? 1.0 : 0.0,
            child: children[i],
          ),
      ],
    );
  }
}